A gas turbine engine includes one or more forward compressor sections for increasing the pressure of an incoming air stream. For example, a turbofan jet engine includes a low pressure compressor (LPC) disposed between fan at the inlet of the engine and a high pressure compressor (HPC). Each compressor includes alternating axial stages of rotors and stators. Each stator is disposed within a circumferential case. Each rotor may include an outer ring of rotating blades; each stator may include a ring of stator segments, with each segment including a shroud connected to an individual vane or a shroud connected to a plurality of vanes. Each shroud may include forward and aft hooks for coupling the segment to the case. More specifically, each shroud may include forward and aft hooks that are received in forward and aft circumferential slots of the case. During assembly, each segment is inserted into the case by inserting the forward and aft hooks of each segment into the corresponding forward and aft circumferential slots of the case. The case may be split into forward and aft portions or the case may be a unitary ring structure.
During normal operation of a gas turbine engine, the combination of temperature variations between the case and the stator segments and the tolerances built into each separate part (i.e., the stator segments and the case) necessitate a suitable cold-clearance gap between adjacent stator segments. Further, aerodynamic loading of each stator segment generates a tangential force approaching 20 lb·f (90 N) per airfoil included in the segment. In order to uniformly distribute the cold-clearance gaps and prevent circumferential sliding of the segments along the case due to aerodynamic and other forces, anti-rotation lugs, bolts or pins may be employed for each segment or one or more anti-rotation lugs may be circumferentially spaced around the case to prevent rotation of the segments along the case. The lugs may be fastened to the case so that the lug is disposed between two segments and contacts a shroud on each of the two segments. The anti-rotation lugs may also facilitate assembly and the positioning of each segment in the case.
One problem associated with this design is that the anti-rotation lug must engage two segments and a portion of the shrouds of each of the two segments must be removed to form a slot or recess for accommodating the lug. Removing part of the shroud, or more specifically, the platform portion of the shroud disposed between the forward and aft hooks, results in removal of part of the one of the forward or aft hooks (more commonly the aft hook). Removing part of the aft hook renders the pair of stator segments less stable within the case which reduces the ability to control the circumferential position of the locking stator segments.